Mounting arrangement for plated piezoelectric crystals



May 20, 1952 R. A. SPEARS 2,597,757

MOUNTING ARRANGEMENT FOR PLATED PIEZOELECTRIC CRYSTALS Filed March 5,1948 I A VE/VT'ORI 2? PH A. SPEARS Patented May 20, 1952 MOUNTINGARRANGEMENT FOR- PLATED PIEZOELECTRIC. CRYSTALS Ralph Aubrey Spears,Liverpool, England, assignor to AutomaticTelephone & Electric CompanyLimited, Liverpool,

company Application England, a British March 5, 1948, Serial No. 13,223

In Great. Britain September 17, 1947 2 Claims. (Cl. 171-327) The presentinvention relates to improvements in mounting arrangements for bar andplate type piezoelectric crystals and more particularly to arrangementsof the type in which wires attached to each of the major surfaces of thecrystal serve both as supports for the crystal and as conductors to theelectrodes adhering to said surfaces.

In a known arrangement of this type the crystal has its two majorsurfaces metallised, with gold for example, to provide electrodes andthe midpoint of each major surface is reinforced by a silver spot whichserves as a base for a soldered butt joint by means of which a thinresilient conducting suspension wire is attached to each major surface,the other end of each wire being attached to a main support so that thecrystal is carried by a two point suspension. The main supports are alsoelectrically conducting and when the unit is mounted in a glassenvelope, of the type used for thermionic Valves, may convenientlyextend to the terminal pins of the envelope.

When a crystal having the above type of two point suspension issubjected to mechanical shock or vibration there is a tendency for it tomove arcuately about its suspension wires and this arcuate movement has,in a known case, been limited by setting suitably slotted mica discstowards the ends of the crystal in such a manner that the crystal isnormally clear of the discs, but upon a predetermined displacement thecrystal strikes one or both of the discs. This arrangement suffers fromthe disadvantage that since the mica discs are rigid the impact of thecrystal on the disc or discs reacts on the suspension wire joints with ashearing action and there is consequently a danger of the jointbreaking. The effect of this shearing action is greater when only oneend of the crystal engages with a mica disc, in which case the crystaltends to pivot about the point of engagement of the crystal with thedisc.

The object of the present invention is to overcome this disadvantage andprovide an improved crystal mounting arrangement wherein the possibilityof breakage of the wire suspension by shearing forces acting on it dueto movement of the crystal about its point of suspension is greatlyreduced.

According to the invention there is provided in a mounting arrangementfor a piezo crystal of rectangular cross-section the combination withelectrode means on each major surface of said crystal and wires attachedto said. electrode the other direction.

means serving both as supports for the crystal and as conductors to saidelectrode means, of resilient means to limit without setting up in sucha manner that the restricting effect does not set up undue reactiveforces in the suspension.

In the preferred form the resilient means comprises bumper members ofresilient wire and substantially U-shaped with the legs of the U lyingin a plane at right angles to the plane of arcuate movement of thecrystal about the wire suspension, said legs being splayed slightlyoutwards and so positioned that the crystal engages with one leg whenrotated slightly in one direction and the other leg when rotatedslightly in This splaying of the legs ensures a point engagement betweenthe bumper member and the crystal, and avoids the possibility of thecrystal electrodes being short circuited.

Alternatively the bumper member may be of resilient non-conductingmaterial for the same purpose of avoiding a short circuit across thecrystal electrodes in which case there is no need for the legs of.,the Uto be splayed.

The invention will be better understood from the following descriptionof one embodiment taken in conjunction with the accompanying drawing ofwhich Fig. 1 shows the preferred arrangement with the crystal element ofthe bar type mounted within a glass envelope.

Fig. 2 is a sectional view in the direction AA in Fig. 1, and Fig. 3 isa sectional view in the direction BB in Fig. 1.

In Fig. l a bar type crystal I0 is supported by two Phosphor bronzesuspension wires H and I2 soldered at points 13 and M to the major facesof the crystal and at their other ends to two main supports I5 and I6.The main supports are located by the mica discs l1 and I8 and strappedto two further supports 21 and 22 by bare wire straps 26 and 21 as shownin Fig. 3. The supports 2| and 22 are welded at their lower end to pinssuch as 23 in the base of the glass envelope 24 and are further 1ocatedat their upper end by a mica plate 25 positioned above disc 18.

Two substantially U-shaped bumper members l9 and 20 of resilient wireare fixed to the main support [B one toward either end of the crystal Inas shown in Fig. 2 so that each leg of the U is located in each caseslightly clear of the side edge of the bar crystal Ill. The bumper members are not a true U shape as with such a shape there is a possibilityof short circuiting the two major surfaces of the crystal, but are of asplayed U shape such that a point engagement 3 between the crysta1 andone leg of the bumper member obtains when the crystal tends to pivotabout its point of suspension l3, l4 and the possibility of shortcircuiting the two faces is minimised.

Alternatively the legs of the bumper may be of a resilientnon-conducting material in which case they need not be splayed as therewill be no risk of short circuiting the major surfaces of the crystal.

oscillatory movement of the crystal in the horizontal plane and arcuatemovement of the crystal about its point of suspension are both limitedby the bumper members 19 and 20; and by reason of the resilient natureof these members the limitation is effected without any impact reactionsetting up shearing forces which would tend to damage the joints betweenthe suspension wires and the crystal itself.

I claim:

1. In a mounting arrangement for piezo crystals of rectangular crosssection, in combination electrode means on each major surface of saidcrystal, rigid electrically conducting supports disposed vertically oneach side of said crystal, horizontal conducting means extending fromsaid vertical supports to a corresponding point on each major surface ofsaid crystal to provide point suspension of and connection to saidcrystal, and substantially U-shaped resilient bumper means mountedcentrally of the curved portion of the U shape on said vertical supportsadjacent the upper and lower extremities of said crystal and extendingacross the path of pivotal movement of said crystal about its point ofsuspension where- 3 by resiliently to limit such movement withoutsetting up undue reactive forces at said point of suspension.

2. In a mounting arrangement for piezo crystals of rectangular crosssection, in combination electrode means on each major surface of saidcrystal, rigid electrically conducting supports disposed vertically oneach side of said crystal, horizontal conducting means extending fromsaid vertical supports to a corresponding point on each major surface ofsaid crystal to provide point suspension of a connection to saidcrystal, and at least one substantially U-shaped resilient bumper membermounted centrally of the curved portion of the U shape on one of saidvertical supports, said bumper member having two legs which extend oneon each side of said crystal across the path of pivotal movement of saidcrystal about its point of suspension whereby resiliently to limit suchmovement without setting up undue reactive forces at said point ofsuspension, and which are splayed toward their extremities so as toensure point engagement of said legs with said crystal in the event ofsuch movement of the crystal.

RALPH AUBREY SPEARS.

REFERENCE S CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,275,122 Ziegler Mar. 3, 19422,371,613 Fair Mar. 20, 1945 2,385,666 Watnobski Sept. 25, 1945

